Mobile communication networks comprise user equipment (e.g., a cell phone, PDA, etc.) that allows a user to communicate with a network via an access point. FIG. 1A illustrates an exemplary wireless cellular network 100, comprising a user equipment (UE) 102 and a plurality of base stations 106a-106g that act as access points for the UE 102 to the cellular network 100.
In LTE and LTE-A systems, before a UE 102 can start transmitting and/or receiving data it must connect to one of the base stations 106a-106g (e.g., an eNodeB) within the cellular network 100. For example, when UE 102 is first turned on or during a handover from one communication cell to another, UE 102 will perform a cell search to find a suitable base station 106. Usually, multiple cells are identified and/or measured for both an initial cell search (e.g., at call setup) and for intra- or inter-frequency neighbor cell searches for cell selection and/or reselection for handover. As described below, initial cell identification, neighbor cell identification, and cell selection or cell reselection, from a plurality of cells, are referred to as a “cell search”.
During the cell search the UE 102 receives signals 108 (e.g., typically based on OFDM) broadcast from a plurality of base stations 106a-106g, respectively located within one or more communication cells 104a-104g, every 5 ms. Based upon the received signal the 102 UE detects a plurality of base stations (e.g., up to 20 or more base stations). Since the UE 102 is associated with a specific operator (e.g., cell phone provider) it is not able to connect with each of the base stations. Rather, after the plurality of base stations are identified, the UE 102 selects one of the base stations broadcasting a strongest signal that allow it to connect.
The signals 108 comprise primary synchronization signal (PSS) and secondary synchronization signal (SSS). For OFDM based LTE/LTE-A, a signal can be, for example, an OFDM symbol in time domain or in frequency domain. FIG. 1B illustrates an exemplary radio frame 110 for an LTE system. As shown in FIG. 1 B, the radio frame 110 comprises a first half frame 112a and a second half frame 112b. Each half frame 112 comprises five sub-frames 114, each of which is broken into two slots 116. For LTE FDD, PSS symbols 120 are located in the last OFDM symbols of the first and 11th slot of each radio frame 110, while SSS symbols 118 immediately precede the PSS symbols 120. The PSS symbols 120 can provide for synchronization between a base station and UE, while SSS symbols 118 provide a UE with a cell group identity, a physical layer identity within a cell group, the CP length, etc.